From 51e1c60cd293a605106e91711cc010f64123293e Mon Sep 17 00:00:00 2001 From: Tao Ma Date: Wed, 28 Sep 2011 10:51:07 +1000 Subject: [PATCH] fs/direct-io.c: salcuate fs_count correctly in get_more_blocks() In get_more_blocks(), we use dio_count to calcuate fs_count and do some tricky things to increase fs_count if dio_count isn't aligned. But actually it still has some corner cases that can't be coverd. See the following example: dio_write foo -s 1024 -w 4096 (direct write 4096 bytes at offset 1024). The same goes if the offset isn't aligned to fs_blocksize. In this case, the old calculation counts fs_count to be 1, but actually we will write into 2 different blocks (if fs_blocksize=4096). The old code just works, since it will call get_block twice (and may have to allocate and create extents twice for filesystems like ext4). So we'd better call get_block just once with the proper fs_count. Signed-off-by: Tao Ma Cc: "Theodore Ts'o" Cc: Christoph Hellwig Cc: Al Viro Signed-off-by: Andrew Morton <> --- fs/direct-io.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/fs/direct-io.c b/fs/direct-io.c index 44a360ca8046..b05f24ee547c 100644 --- a/fs/direct-io.c +++ b/fs/direct-io.c @@ -569,9 +569,8 @@ static int get_more_blocks(struct dio *dio) int ret; struct buffer_head *map_bh = &dio->map_bh; sector_t fs_startblk; /* Into file, in filesystem-sized blocks */ + sector_t fs_endblk; /* Into file, in filesystem-sized blocks */ unsigned long fs_count; /* Number of filesystem-sized blocks */ - unsigned long dio_count;/* Number of dio_block-sized blocks */ - unsigned long blkmask; int create; /* @@ -582,11 +581,8 @@ static int get_more_blocks(struct dio *dio) if (ret == 0) { BUG_ON(dio->block_in_file >= dio->final_block_in_request); fs_startblk = dio->block_in_file >> dio->blkfactor; - dio_count = dio->final_block_in_request - dio->block_in_file; - fs_count = dio_count >> dio->blkfactor; - blkmask = (1 << dio->blkfactor) - 1; - if (dio_count & blkmask) - fs_count++; + fs_endblk = (dio->final_block_in_request - 1) >> dio->blkfactor; + fs_count = fs_endblk - fs_startblk + 1; map_bh->b_state = 0; map_bh->b_size = fs_count << dio->inode->i_blkbits; -- 2.39.2